George Koonce was born in April 1818 in Ohio to Nicholas and Elizabeth Koonce. Soon after his birth, the family moved to Harper's Ferry, Virginia. He was married twice, first to Emily Piles, and then to Bettie Ellen Brittain. Koonce had at least one son, George William Koonce (b. 1840).
On April 18, 1861, less than a day after Virginia seceded from the Union, Lieutenant Roger Jones was stationed at Harper's Ferry, Virginia, with a company of forty-two regular United States soldiers. Upon learning of the approach of Confederate soldiers, whose intent was to take over the armory, he made preparations for its defense, calling upon the local citizens for volunteer aid. Many responded, including George Koonce, a former town constable according to the 1860 census and Justice of the Peace for Jefferson County, who led the local men against the Virginia army of 2,000 soldiers. Koonce and his fellow citizens halted the larger Virginia army at Smallwood's Ridge, near Bolivar. Meanwhile, Lieutenant Jones, acting on orders received from Washington, set fire to the armory and arsenal and, with his men, retreated northward. Koonce and his fellow volunteers did not return to Harper's Ferry until it had once again fallen into the hands of the U. S. government in 1862.
In June 1861, Koonce represented Jefferson County at the Second Wheeling Convention to vote on the secession of western Virginia. However, Koonce, who harbored ill feelings towards the Confederacy after the events of April 1861 and who was a Unionist, was not representative of the majority of citizens of Jefferson County, most of whom supported the Confederacy.
Koonce lost his home and his business as a result of his involvement in the April 1861 fight. During the Civil War, he operated a general store in Harper's Ferry with a Mr. Horner from 1863 to 1864.
Following the war, Koonce became active in politics once again, serving as a member of the West Virginia House of Delegates (1865-1867) and a member of the West Virginia Senate (1870-1871), running on the Radical ticket. He was also a member of the Independent Order of Odd Fellows.
George Koonce died in Halltown, West Virginia, in 1908 at the age of ninety.